In Webstyle, a button is displayed in the selected state when the url that the button is linked to is the same address upon which the navbar is being viewed.

The state is only supported when no sub menus have been applied to the navbar.

I recommend you post your url allowing the problem to be viewed. From Antony's response, its clear that they do monitor the forum so im sure Xara will view the problem

Additionally post a support ticket allowing the support team to reply